Studies have shown that a not inconsiderable number of traffic accidents are caused by drowsiness of the driver. It is therefore very important to be able to detect and, if necessary, also predict the state of drowsiness of a driver. Drowsiness limits the driving fitness to a degree similar to alcohol. A driver who is drowsy is unable to concentrate well, reacts slower and overestimates his/her own abilities. Methods and devices are already in use, which determine the state of drowsiness of the driver as a function of steering angle changes and ability to stay in the lane. Products are also available, which issue a warning when the eye closes. Thus, for example, U.S. Patent Application Publication No. 2004/0233061 A1 describes a monitoring method, in which the movements of an eyelid are monitored in order to detect a blinking by the driver indicating drowsiness.